Generally speaking, due to errors in manufacturing processes, differences exist in parameters of the same type of components among power supply units (PSUs). For a capacitor of a PSU, error in capacitance of the capacitor affects its voltage drop. The variation in the voltage drop influences the performance of the PSU, and lowers reliability of the PSU. In addition, a larger margin for error should be considered in designing the PSU for overcoming the issue of insufficient accuracy of voltage across the capacitor. The capacitor of the PSU is often referred to as a “bulk capacitor”. The voltage across the capacitor of the PSU is often referred to as “bulk voltage”. It is noted that reliability described here refers for example to the following: efficiency of the PSU, and precision of indicative characteristics of the PSU, such as hold-up time, regulation, stress, thermal, etc.
During the process of manufacturing conventional PSUs, in order to solve the problem of inaccuracy of the bulk voltage with respect to that according to PSU product specifications, the actual bulk voltage is measured by using a voltmeter in a production line for compensation of errors so as to calibrate the actual bulk voltage.
However, since the bulk voltage usually cannot be measured directly at an output port of the conventional PSU, a housing of the conventional PSU must be opened for the measurement of the bulk voltage. Opening of the housing might endanger operators on the production line due to possible electric shock from high voltage of the PSU, and could cause damages to the PSU. Moreover, it increases the manufacturing time. Besides, though the conventional PSUs have been calibrated during production, the reliability and performance thereof might still deviate from the PSU specifications due to variation in the bulk voltage caused by other abnormal factors.